670 



STRUCTURE OF THE BULB, PONS, AND MID-BRAIN [CH. XLVL 



direct cerebellar tract of the cord also passes into the restiform body. 

 Its fibres terminate by arborisations round Purkinje's cells in the 

 vermis of the cerebellum. The continuation of the tract of Gowers 

 lies just dorsal to the olivary body. The funiculus solitarius and 

 nucleus ambiguus, also seen in this section, will be considered in 

 our account of the origin of the ninth and tenth cranial nerves. 



Fourth section (fig. 413). This is taken through the middle of 

 the pons, and shows much the same kind of arrangement as in the 

 upper part of the bulb. The general appearance of the section is, 

 however, modified by a number of transversely coursing bundles of 



FIG. 413. Section across the pons, about the middle of the fourth ventricle, py, Pyramidal bundles ; 

 po., transverse fibres passing po l behind, andpo 2 , in front of py; r., raphe ; o.s., superior olive; 

 a.V., bundles of motor root of V. nerve enclosed in a prolongation of the substance of Rolando; t, 

 trapezium ; VI., the sixth nerve, n.VL, its nucleus ; VII., facial nerve; Vll.a., intermediate por- 

 tion, n.VIL, its nucleus; VIII., auditory nerve ; n.VIIL, Deiters' nucleus, formerly called the 

 lateral nucleus of the auditory. (After Quain.) 



fibres, most of which are passing to the cerebellar hemispheres and 

 form the middle cerebellar peduncles. Intermingled with these is a 

 considerable amount of grey matter (nuclei pontis). 



From the cells of the nuclei pontis, the fibres of the middle 

 peduncle take origin, and many fibres and collaterals of the pyramidal 

 tract arborise around them. The continuation of the pyramids (py) is 

 imbedded between these transverse bundles. The pyramidal fibres 

 which terminate in the pons are situated postero-laterally, and are 

 spoken of as cortico-pontine in contradistinction with those of the 

 pyramidal tract proper (cortico-spinal) which pass down through the 

 bulb to the cord. 



The pyramidal bundles are separated from the reticular formation 



